Alkyl amidopropyl betaines in general and cocoamidopropylbetaine (CAPB, CAS 61789-40-0) in particular are known for their mildness and hence are very widely used in personal care and consumer products [“Encyclopedia of conditioning rinse ingredients” ed. A. L. L. Hunting, Micelle Press, London (1987), p. 125].
As a result of their superior performance, biodegradability and low toxicology profile, they are used on huge scale in cosmetic industry [X. Domingo, “Amphoteric Surfactants” ed. E. G. Lomax, Surfactant Science Series, Marcel Dekker Inc., New York, (1996), Vol. 59, p. 75 and J. G. Weers, J. F. Rathman, F. U. Axe, C. A. Crichlow, L. D. Foland, D. R. Scheuing, R. J. Wiersema and A. G. Zielske, Langmuir, 7, 854-867, (1991)].
A conventional commercial betaine composition typically has the following compositions:
Water64%by weightBetaine28-29%by weightNaCl5-6%by weightGlycerin0.3%by weightFatty acid0.5%by weightAmidoamineca. 0.3%by weightTotal solids contentca. 36%by weight
The solids content represents the sum of the components other than water. The proportions of betaine and sodium chloride arise out of the stoichiometry of the reaction of the fatty amide with tertiary amino group (amidoamine) and sodium chloroacetate according to the equation given below.

A small amount of amidoamine normally remains in the product because the quaternization reaction is incomplete. This proportion can, however, be further reduced by an adapted stoichiometry and reaction procedure. The further typical components like glycerin and fatty acids listed originate from the synthesis of the amidoamine. Small amounts of fatty acids (0.5%) in the betaine composition results from synthesis of amidoamine from the corresponding fatty acid and 3-N,N-dimethylaminopropylamine. Glycerin is present in the betaine composition if the amidoamine is synthesized from triglycerides (coconut or palm oil) and 3-N,N-dimethylaminopropylamine.
It is well known that composition of betaines of the aforementioned type is liquid only below a particular concentration of total solids. For example, at ambient temperature a composition of a betaine of Formula I derived from coconut fatty acids solidifies at a solids content of about 40% by weight. For this reason, conventional, commercial, aqueous solutions of coconut amidopropylbetaine, derived from coconut fatty acids, have total solids concentrations below 40% by weight and in most cases about 35-36% by weight. The maximum achievable concentration of a flowable solution of a betaine decreases as the number of carbon atoms is increased. If the fatty acid mixture contains a higher proportion of unsaturated fatty acids, the concentrations achievable frequently are comparatively higher than those achievable with saturated fatty acids.
Several attempts have been made to create betaines (Formula I) of higher concentration primarily because it has been shown that aqueous betaine composition of higher concentrations is self-preserving. The second obvious motive for preparing betaines of higher concentration is low cost of transportation. U.S. Pat. No. 4,243,549 (1981) describes preparation of high active betaines (33.5% by weight) by blending equivalent amount of ethoxylated alkyl sulphate, the anionic surfactant. Flowable and pumpable high active betaines are reported in German patent DE 3613944. The synthesis described in this patent involves use of solvent and azeotropic removal of water. Another German patent DE 3726322 reveals use of highly acidic pH to create betaines of higher concentration. Use of 3 to 20% by weight of nonionic surfactant is taught by German patent DE 3826654 for making betaines of higher concentration. Reference is made to U.S. Pat. No. 5,354,906 (1994) according to which upto 36% by weight active betaines are produced by addition of 1 to 3% by weight of fatty acids. This results in overall solids content of at least 40% by weight [DE 4207386 (1993); EP 560114 (1993)]. DE 19523477 reports the process of making betaines with active content of 40 to 45% by weight using quaternised salts of tertiary amidoamines that are synthesized from 3-N,N-dimethylaminopropylamine and polycarboxylic acids. Flowable betaines of total solids content of 40-55% by weight are made by incorporation of 1 to 10% by weight of hydroxy carboxylic acids [DE 4408183]. Finally, inclusion of mixture of fatty acids and ethoxylated cocomono glycerides also result in achieving betaines of high activity [DE 4408228].
Thus, it makes sense to create industrially feasible alkylamidopropylbetaines (Formula I) of higher concentration to save on freight charges and to render them self-preserving. The self-preserving nature of high active betaines has been established by performing ‘preservation loading test’ using various types of micro organisms [U.S. Pat. No. 5,354,906 (1994)]. It is an object of the present invention to provide a high active aqueous betaine composition comprising a betaine of the general Formula I with less than 5.0 ppm of free sodium monochloroacetate, a totally undesirable impurity.
It is an object of the present invention to provide a process for preparing a high active aqueous betaine composition comprising a betaine of the general Formula I which obviates steps like filtration, concentration and use of organic solvents for making high active betaines.
It is a further object of the present invention to provide an aqueous betaine composition comprising a betaine of the general Formula I which is self-preserving.